Chiral C2-Symmetric Diimines with 4,5-Diazafluorene Units.

A synthetic approach to a new group of stable chiral C2-symmetric diimines with the 4,5-diazafluorene core has been developed based on condensation of dipinodiazafluorene with aromatic diamines. The chemical structures of new compounds were proven by spectroscopic methods and X-ray crystallography. All the compounds form solvates with organic solvents (chloroform, benzene, 1,4-dioxane) and water. Specific spectral data of the new compounds are explained using calculated data (DFT). Diimines of the pinodiazafluorene series give colored reactions with transition metal ions and can be regarded as prospective polydentate ligands with interesting luminescent and chiroptical properties.

Bis(DL-cysteinium) oxalate.

In the title compound, 2C3H8NO2S+.C2O4(2-), the oxalate anion occupies an inversion centre and is coordinated to cysteine molecules of different chirality (L and D) via O-H...O and N-H...O hydrogen bonds, the resulting cysteine-oxalate stoichiometry in the crystal structure being 2:1. The oxalate anion is completely deprotonated, whereas cysteine has a positively charged -NH3+ group and a neutral protonated carboxyl group. The structure is built from infinite hydrogen-bonded triple layers, consisting of an oxalate layer in the middle with layers of L- and D-cysteine molecules on either side. The thiol groups are at the external sides of the layers and form S-H...O hydrogen bonds with the carboxyl groups of neighbouring cysteine molecules. An interesting feature of the structure is the occurrence of short S...S contacts between SH groups of molecules in neighbouring layers, which form not S-H...S but S-H...O intermolecular hydrogen bonds. Due to the effects of crystal packing and intermolecular hydrogen-bond formation, the conformation of the cysteine cation in the title structure is different from that calculated theoretically for an individual cation, as well as from those of cysteine zwitterions in crystals of pure cysteine.